This invention relates to a telephone line test device and more particularly to a small self-contained line-powered telephone line test device to indicated qualification of a subscriber loop telephone circuit to minimum requirements for loop current, signal loss, circuit noise and power influence noise.
As a result of recent reorganization of U.S. domestic and international telephone companies and systems pursuant to court orders, telephone customers are allowed much greater latitude in the types of equipment they are allowed to attach or plug into the commercial telephone network. The changes have brought about a division of responsibility for maintenance of the telephone system between the subscriber, responsible for equipment and lines within the network embodied in his private structures and premises and the telephone companies supplying to their subscribers the service lines to the central office switching, interconnect and network services and responsible for the maintenance and repair of service lines and equipment used by them to provide subscribers with the interconnect switching and network services.
Thus, it has become desirable to isolate and separately test the telephone equipment lines of the telephone company network and lines and equipment of the customer's "internal" network. Testing equipment of the general type herein disclosed for the testing of telephone lines and equipment is typified by the disclosures of the following U.S. patents.
U.S. Pat. No. 4,912,755 to Blood, et al. shows a hand-held multiple test device for conducting line tests at subscriber premises. The device is powered from self-contained batteries, not from the phone lines. It uses multiple individual and lockable exclusive push button switches for selecting functions to check current in the central office line with a 600 ohm and a 900 ohm termination (LCD indicator), to check ground start and to check line current with customer equipment "off hook." Also available are tone generation functions for line identification and fault location. No specific noise test is indicated.
U.S. Pat. No. 4,051,333 to Schomburg provides a line voltage tester installed as part of a telephone lineman's handset. Test results are indicated by a first tone, a second tone, both tones or no tone in the ear phone. The device is powered by line energy in capacitor storage.
U.S. Pat. No. 4,055,733 to Holsinger, et al. shows a test device to be switched between multiple lines to compare the signal power on each line with a reference. The comparator and other operating circuits are not line powered. LED's indicate whether line power is over or under reference in stepped magnitudes. Blanking circuits allow only one diode to light at any one time.
Feldman, et al. U.S. Pat. No. 4,600,810 discloses a go-no go tester with a lit LED indicating nominal 8 volt tip-to-ring voltage on a phone line terminated with 400 ohms. The internal amplifier is "powered" from the line under test but without isolation.
U.S. Pat. No. 4,841,559 to Curtis uses a 2-pole, 5-position switch to provide various line checks on both company service lines and the customer's network. LED's indicate go-no go test results; the amplifiers used on some tests are powered from the service line but without isolation or regulation.
Dash U.S. Pat. No. 4,825,458 shows equipment for testing subscriber equipment to prevent damage to the service network.
Rummel U.S. Pat. No. 3,508,139 provides an electronic "line holding" circuit that draws a constant current to activate holding relays while presenting "infinite" impedance to AC test signals for line loss check. The circuit is not used as a power supply for other test circuits.
U.S. Pat. No. 4,522,996 to DeBergh provides a device for the measurement of noise on a telephone line that is "in use" by sampling the signal level over a number of periods. The device is externally powered.
Amadio, et al. U.S. Pat. No. 4,751,724 discloses a device for automatic measurement and comparison of resistances (a bridge circuit) to locate faults on a line. The device uses an external power source.
Garrett, et al. U.S. Pat. No. 3,711,661 shows a multi-function automatic test device for use at the central office. The device does not use line voltages for power.
U.S. Pat. No. 4,969,179 to Kanare, et al. discloses a battery-powered line monitoring device for subscribers to provide a light and/or sonic alarm in the event of low voltage on the line, an open or a short on the line.
U.S. Pat. No. 4,720,845 to Lechner, et al. shows a surge protection device for a subscriber line interconnect circuit. The device is not a test circuit in the usual sense.
U S. Pat. No. 4,544,807 to Sers discloses a fault detection and locating circuit that can be placed at the interface between customer-provided circuits and equipment and the telephone company's circuits and equipment. No noise testing is provided.
The device of U.S. Pat. No. 4,564,728 to Romano is a simple plug-in device to detect the presence of DC voltage on a telephone line.
Ross U.S. Pat. No. 4,827,498 shows a DC current detection device to be inserted at the customer/company line interface to indicate the location of a fault according to a current flow detector.
In contrast to the foregoing devices, the present invention provides a telephone line testing device capable of four different tests selectable through a slide switching means with test results indicated by a three-color light-emitting diode as "pass", "fail" or "marginal." The tester is small, hand held and light weight and requires no batteries or separate power supply in that it is powered from the telephone lines under test through a shunt-regulated supply circuit that does not adversely affect test results.
It is an object then of the present invention to provide a telephone line test device that is hand held, light weight and requires no batteries.
It is a further object of this invention to provide a telephone line testing device capable of selectively providing telephone line tests for central office supplied loop current, AC current loss, circuit noise and power influence over longitudinal noise.
It is a still further object of the present invention to provide a telephone line testing device that is powered by line current through a unique shunt-regulated supply circuit leaving unaffected the line parameters to be tested.